Are you having the problem in EndNote referencing software where you can’t enter any text into the “Sync this EndNote Library” field, and you have synced your library in the past? This is a known issue that has been in EndNote version X20, X9, X8, X7 etc. Below I describe the solution that worked for me.
First, it’s worth knowing that EndNote requires a local file and folder on your computer to sync any updates to, and from, EndNote online. You’ll typically have a file ending with the extension .enl as well as a folder ending with .Data.
The problem where you can’t enter the path to your .enl file in the “Sync this EndNote Library” field” is one of poor design and testing by EndNote. I mention this because you’re able to enter your cursor in this field which typically implies that you may type in this field or select a location of your .enl file. You cannot enter text into this field … EndNote automatically populates this field.
The trick is, in EndNote, click file and then new and create a new empty library. Now click Edit, Preferences, then the “Sync this EndNote Library” should be populated with the new .enl file name (if not then click ‘Enable Sync’). Your new .enl file will now be populated with the content of your online EndNote library.